PHYTOGENESIS. 251 
I return then to my question: what is the meaning of to 
grow? In hackneyed phrase we are told, “ To grow signifies 
merease of the mass of an individual, and takes place in the 
inorganic world by juxtaposition, in the organic by intus- 
susception.” Have we gained anything for vegetable physi- 
ology by this reply? Ithink not. If the plant is to grow 
by intussusception, then I say it consists of an aggregate of 
single, independent, organic molecules, the cells; it increases 
its mass by new cells being deposited upon those already ex- 
isting ; consequently by juxtaposition. But the single cell in 
the progress of its expansion, which frequently reaches an 
enormous bulk in comparison with its original size (I will 
merely remind the reader of the pollen-tubes), also increases 
in substance in the interior of its membrane, and by this 
means also the mass of the entire plant is increased ; it con- 
sequently grows by intussusception also. Finally, after a certain 
period the cell deposits new organic material in layers upon its 
primitive membrane ; thus another form of juxtaposition, which 
still, however, belongs to the cycle of vegetable vitality. It 
hence becomes readily apparent that, in respect to scientific 
botany, the idea “grow” still requires a new foundation in 
order to be capable of being applied with certainty. 
Of the three instances just cited, the second and third 
belong more to the individual life of the cells, and are of 
secondary importance only, as respects the idea of the whole 
plant, regarded as an organism composed of a certain number of 
cells. The plant considered in its totality increases its mass, that 
is, the number of the cells composing it, in the first way only. 
We must therefore here discriminate three processes essen- 
tially distinct from each other in a physiological sense, which, 
when strictly regarded, scarcely find an analogy in the other 
kingdoms of nature. 
1. The plant grows, that is, it produces the number of cells 
allotted to it. 
2. The plant unfolds itself by the expansion and develop- 
ment of the cells already formed. It is this phenomenon 
especially, one altogether peculiar to plants, which, because it 
depends upon the fact of their being composed of cells, can 
never occur in any, not even the most remote form in crystals 
or animals. 
